linux/fs/eventpoll.c
Roman Penyaev a218cc4914 epoll: use rwlock in order to reduce ep_poll_callback() contention
The goal of this patch is to reduce contention of ep_poll_callback()
which can be called concurrently from different CPUs in case of high
events rates and many fds per epoll.  Problem can be very well
reproduced by generating events (write to pipe or eventfd) from many
threads, while consumer thread does polling.  In other words this patch
increases the bandwidth of events which can be delivered from sources to
the poller by adding poll items in a lockless way to the list.

The main change is in replacement of the spinlock with a rwlock, which
is taken on read in ep_poll_callback(), and then by adding poll items to
the tail of the list using xchg atomic instruction.  Write lock is taken
everywhere else in order to stop list modifications and guarantee that
list updates are fully completed (I assume that write side of a rwlock
does not starve, it seems qrwlock implementation has these guarantees).

The following are some microbenchmark results based on the test [1]
which starts threads which generate N events each.  The test ends when
all events are successfully fetched by the poller thread:

 spinlock
 ========

 threads  events/ms  run-time ms
       8       6402        12495
      16       7045        22709
      32       7395        43268

 rwlock + xchg
 =============

 threads  events/ms  run-time ms
       8      10038         7969
      16      12178        13138
      32      13223        24199

According to the results bandwidth of delivered events is significantly
increased, thus execution time is reduced.

This patch was tested with different sort of microbenchmarks and
artificial delays (e.g.  "udelay(get_random_int() & 0xff)") introduced
in kernel on paths where items are added to lists.

[1] https://github.com/rouming/test-tools/blob/master/stress-epoll.c

Link: http://lkml.kernel.org/r/20190103150104.17128-5-rpenyaev@suse.de
Signed-off-by: Roman Penyaev <rpenyaev@suse.de>
Cc: Davidlohr Bueso <dbueso@suse.de>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-03-07 18:32:01 -08:00

2404 lines
65 KiB
C

/*
* fs/eventpoll.c (Efficient event retrieval implementation)
* Copyright (C) 2001,...,2009 Davide Libenzi
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* Davide Libenzi <davidel@xmailserver.org>
*
*/
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/sched/signal.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/signal.h>
#include <linux/errno.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/poll.h>
#include <linux/string.h>
#include <linux/list.h>
#include <linux/hash.h>
#include <linux/spinlock.h>
#include <linux/syscalls.h>
#include <linux/rbtree.h>
#include <linux/wait.h>
#include <linux/eventpoll.h>
#include <linux/mount.h>
#include <linux/bitops.h>
#include <linux/mutex.h>
#include <linux/anon_inodes.h>
#include <linux/device.h>
#include <linux/uaccess.h>
#include <asm/io.h>
#include <asm/mman.h>
#include <linux/atomic.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/compat.h>
#include <linux/rculist.h>
#include <net/busy_poll.h>
/*
* LOCKING:
* There are three level of locking required by epoll :
*
* 1) epmutex (mutex)
* 2) ep->mtx (mutex)
* 3) ep->lock (rwlock)
*
* The acquire order is the one listed above, from 1 to 3.
* We need a rwlock (ep->lock) because we manipulate objects
* from inside the poll callback, that might be triggered from
* a wake_up() that in turn might be called from IRQ context.
* So we can't sleep inside the poll callback and hence we need
* a spinlock. During the event transfer loop (from kernel to
* user space) we could end up sleeping due a copy_to_user(), so
* we need a lock that will allow us to sleep. This lock is a
* mutex (ep->mtx). It is acquired during the event transfer loop,
* during epoll_ctl(EPOLL_CTL_DEL) and during eventpoll_release_file().
* Then we also need a global mutex to serialize eventpoll_release_file()
* and ep_free().
* This mutex is acquired by ep_free() during the epoll file
* cleanup path and it is also acquired by eventpoll_release_file()
* if a file has been pushed inside an epoll set and it is then
* close()d without a previous call to epoll_ctl(EPOLL_CTL_DEL).
* It is also acquired when inserting an epoll fd onto another epoll
* fd. We do this so that we walk the epoll tree and ensure that this
* insertion does not create a cycle of epoll file descriptors, which
* could lead to deadlock. We need a global mutex to prevent two
* simultaneous inserts (A into B and B into A) from racing and
* constructing a cycle without either insert observing that it is
* going to.
* It is necessary to acquire multiple "ep->mtx"es at once in the
* case when one epoll fd is added to another. In this case, we
* always acquire the locks in the order of nesting (i.e. after
* epoll_ctl(e1, EPOLL_CTL_ADD, e2), e1->mtx will always be acquired
* before e2->mtx). Since we disallow cycles of epoll file
* descriptors, this ensures that the mutexes are well-ordered. In
* order to communicate this nesting to lockdep, when walking a tree
* of epoll file descriptors, we use the current recursion depth as
* the lockdep subkey.
* It is possible to drop the "ep->mtx" and to use the global
* mutex "epmutex" (together with "ep->lock") to have it working,
* but having "ep->mtx" will make the interface more scalable.
* Events that require holding "epmutex" are very rare, while for
* normal operations the epoll private "ep->mtx" will guarantee
* a better scalability.
*/
/* Epoll private bits inside the event mask */
#define EP_PRIVATE_BITS (EPOLLWAKEUP | EPOLLONESHOT | EPOLLET | EPOLLEXCLUSIVE)
#define EPOLLINOUT_BITS (EPOLLIN | EPOLLOUT)
#define EPOLLEXCLUSIVE_OK_BITS (EPOLLINOUT_BITS | EPOLLERR | EPOLLHUP | \
EPOLLWAKEUP | EPOLLET | EPOLLEXCLUSIVE)
/* Maximum number of nesting allowed inside epoll sets */
#define EP_MAX_NESTS 4
#define EP_MAX_EVENTS (INT_MAX / sizeof(struct epoll_event))
#define EP_UNACTIVE_PTR ((void *) -1L)
#define EP_ITEM_COST (sizeof(struct epitem) + sizeof(struct eppoll_entry))
struct epoll_filefd {
struct file *file;
int fd;
} __packed;
/*
* Structure used to track possible nested calls, for too deep recursions
* and loop cycles.
*/
struct nested_call_node {
struct list_head llink;
void *cookie;
void *ctx;
};
/*
* This structure is used as collector for nested calls, to check for
* maximum recursion dept and loop cycles.
*/
struct nested_calls {
struct list_head tasks_call_list;
spinlock_t lock;
};
/*
* Each file descriptor added to the eventpoll interface will
* have an entry of this type linked to the "rbr" RB tree.
* Avoid increasing the size of this struct, there can be many thousands
* of these on a server and we do not want this to take another cache line.
*/
struct epitem {
union {
/* RB tree node links this structure to the eventpoll RB tree */
struct rb_node rbn;
/* Used to free the struct epitem */
struct rcu_head rcu;
};
/* List header used to link this structure to the eventpoll ready list */
struct list_head rdllink;
/*
* Works together "struct eventpoll"->ovflist in keeping the
* single linked chain of items.
*/
struct epitem *next;
/* The file descriptor information this item refers to */
struct epoll_filefd ffd;
/* Number of active wait queue attached to poll operations */
int nwait;
/* List containing poll wait queues */
struct list_head pwqlist;
/* The "container" of this item */
struct eventpoll *ep;
/* List header used to link this item to the "struct file" items list */
struct list_head fllink;
/* wakeup_source used when EPOLLWAKEUP is set */
struct wakeup_source __rcu *ws;
/* The structure that describe the interested events and the source fd */
struct epoll_event event;
};
/*
* This structure is stored inside the "private_data" member of the file
* structure and represents the main data structure for the eventpoll
* interface.
*/
struct eventpoll {
/*
* This mutex is used to ensure that files are not removed
* while epoll is using them. This is held during the event
* collection loop, the file cleanup path, the epoll file exit
* code and the ctl operations.
*/
struct mutex mtx;
/* Wait queue used by sys_epoll_wait() */
wait_queue_head_t wq;
/* Wait queue used by file->poll() */
wait_queue_head_t poll_wait;
/* List of ready file descriptors */
struct list_head rdllist;
/* Lock which protects rdllist and ovflist */
rwlock_t lock;
/* RB tree root used to store monitored fd structs */
struct rb_root_cached rbr;
/*
* This is a single linked list that chains all the "struct epitem" that
* happened while transferring ready events to userspace w/out
* holding ->lock.
*/
struct epitem *ovflist;
/* wakeup_source used when ep_scan_ready_list is running */
struct wakeup_source *ws;
/* The user that created the eventpoll descriptor */
struct user_struct *user;
struct file *file;
/* used to optimize loop detection check */
int visited;
struct list_head visited_list_link;
#ifdef CONFIG_NET_RX_BUSY_POLL
/* used to track busy poll napi_id */
unsigned int napi_id;
#endif
};
/* Wait structure used by the poll hooks */
struct eppoll_entry {
/* List header used to link this structure to the "struct epitem" */
struct list_head llink;
/* The "base" pointer is set to the container "struct epitem" */
struct epitem *base;
/*
* Wait queue item that will be linked to the target file wait
* queue head.
*/
wait_queue_entry_t wait;
/* The wait queue head that linked the "wait" wait queue item */
wait_queue_head_t *whead;
};
/* Wrapper struct used by poll queueing */
struct ep_pqueue {
poll_table pt;
struct epitem *epi;
};
/* Used by the ep_send_events() function as callback private data */
struct ep_send_events_data {
int maxevents;
struct epoll_event __user *events;
int res;
};
/*
* Configuration options available inside /proc/sys/fs/epoll/
*/
/* Maximum number of epoll watched descriptors, per user */
static long max_user_watches __read_mostly;
/*
* This mutex is used to serialize ep_free() and eventpoll_release_file().
*/
static DEFINE_MUTEX(epmutex);
/* Used to check for epoll file descriptor inclusion loops */
static struct nested_calls poll_loop_ncalls;
/* Slab cache used to allocate "struct epitem" */
static struct kmem_cache *epi_cache __read_mostly;
/* Slab cache used to allocate "struct eppoll_entry" */
static struct kmem_cache *pwq_cache __read_mostly;
/* Visited nodes during ep_loop_check(), so we can unset them when we finish */
static LIST_HEAD(visited_list);
/*
* List of files with newly added links, where we may need to limit the number
* of emanating paths. Protected by the epmutex.
*/
static LIST_HEAD(tfile_check_list);
#ifdef CONFIG_SYSCTL
#include <linux/sysctl.h>
static long zero;
static long long_max = LONG_MAX;
struct ctl_table epoll_table[] = {
{
.procname = "max_user_watches",
.data = &max_user_watches,
.maxlen = sizeof(max_user_watches),
.mode = 0644,
.proc_handler = proc_doulongvec_minmax,
.extra1 = &zero,
.extra2 = &long_max,
},
{ }
};
#endif /* CONFIG_SYSCTL */
static const struct file_operations eventpoll_fops;
static inline int is_file_epoll(struct file *f)
{
return f->f_op == &eventpoll_fops;
}
/* Setup the structure that is used as key for the RB tree */
static inline void ep_set_ffd(struct epoll_filefd *ffd,
struct file *file, int fd)
{
ffd->file = file;
ffd->fd = fd;
}
/* Compare RB tree keys */
static inline int ep_cmp_ffd(struct epoll_filefd *p1,
struct epoll_filefd *p2)
{
return (p1->file > p2->file ? +1:
(p1->file < p2->file ? -1 : p1->fd - p2->fd));
}
/* Tells us if the item is currently linked */
static inline int ep_is_linked(struct epitem *epi)
{
return !list_empty(&epi->rdllink);
}
static inline struct eppoll_entry *ep_pwq_from_wait(wait_queue_entry_t *p)
{
return container_of(p, struct eppoll_entry, wait);
}
/* Get the "struct epitem" from a wait queue pointer */
static inline struct epitem *ep_item_from_wait(wait_queue_entry_t *p)
{
return container_of(p, struct eppoll_entry, wait)->base;
}
/* Get the "struct epitem" from an epoll queue wrapper */
static inline struct epitem *ep_item_from_epqueue(poll_table *p)
{
return container_of(p, struct ep_pqueue, pt)->epi;
}
/* Tells if the epoll_ctl(2) operation needs an event copy from userspace */
static inline int ep_op_has_event(int op)
{
return op != EPOLL_CTL_DEL;
}
/* Initialize the poll safe wake up structure */
static void ep_nested_calls_init(struct nested_calls *ncalls)
{
INIT_LIST_HEAD(&ncalls->tasks_call_list);
spin_lock_init(&ncalls->lock);
}
/**
* ep_events_available - Checks if ready events might be available.
*
* @ep: Pointer to the eventpoll context.
*
* Returns: Returns a value different than zero if ready events are available,
* or zero otherwise.
*/
static inline int ep_events_available(struct eventpoll *ep)
{
return !list_empty_careful(&ep->rdllist) ||
READ_ONCE(ep->ovflist) != EP_UNACTIVE_PTR;
}
#ifdef CONFIG_NET_RX_BUSY_POLL
static bool ep_busy_loop_end(void *p, unsigned long start_time)
{
struct eventpoll *ep = p;
return ep_events_available(ep) || busy_loop_timeout(start_time);
}
/*
* Busy poll if globally on and supporting sockets found && no events,
* busy loop will return if need_resched or ep_events_available.
*
* we must do our busy polling with irqs enabled
*/
static void ep_busy_loop(struct eventpoll *ep, int nonblock)
{
unsigned int napi_id = READ_ONCE(ep->napi_id);
if ((napi_id >= MIN_NAPI_ID) && net_busy_loop_on())
napi_busy_loop(napi_id, nonblock ? NULL : ep_busy_loop_end, ep);
}
static inline void ep_reset_busy_poll_napi_id(struct eventpoll *ep)
{
if (ep->napi_id)
ep->napi_id = 0;
}
/*
* Set epoll busy poll NAPI ID from sk.
*/
static inline void ep_set_busy_poll_napi_id(struct epitem *epi)
{
struct eventpoll *ep;
unsigned int napi_id;
struct socket *sock;
struct sock *sk;
int err;
if (!net_busy_loop_on())
return;
sock = sock_from_file(epi->ffd.file, &err);
if (!sock)
return;
sk = sock->sk;
if (!sk)
return;
napi_id = READ_ONCE(sk->sk_napi_id);
ep = epi->ep;
/* Non-NAPI IDs can be rejected
* or
* Nothing to do if we already have this ID
*/
if (napi_id < MIN_NAPI_ID || napi_id == ep->napi_id)
return;
/* record NAPI ID for use in next busy poll */
ep->napi_id = napi_id;
}
#else
static inline void ep_busy_loop(struct eventpoll *ep, int nonblock)
{
}
static inline void ep_reset_busy_poll_napi_id(struct eventpoll *ep)
{
}
static inline void ep_set_busy_poll_napi_id(struct epitem *epi)
{
}
#endif /* CONFIG_NET_RX_BUSY_POLL */
/**
* ep_call_nested - Perform a bound (possibly) nested call, by checking
* that the recursion limit is not exceeded, and that
* the same nested call (by the meaning of same cookie) is
* no re-entered.
*
* @ncalls: Pointer to the nested_calls structure to be used for this call.
* @nproc: Nested call core function pointer.
* @priv: Opaque data to be passed to the @nproc callback.
* @cookie: Cookie to be used to identify this nested call.
* @ctx: This instance context.
*
* Returns: Returns the code returned by the @nproc callback, or -1 if
* the maximum recursion limit has been exceeded.
*/
static int ep_call_nested(struct nested_calls *ncalls,
int (*nproc)(void *, void *, int), void *priv,
void *cookie, void *ctx)
{
int error, call_nests = 0;
unsigned long flags;
struct list_head *lsthead = &ncalls->tasks_call_list;
struct nested_call_node *tncur;
struct nested_call_node tnode;
spin_lock_irqsave(&ncalls->lock, flags);
/*
* Try to see if the current task is already inside this wakeup call.
* We use a list here, since the population inside this set is always
* very much limited.
*/
list_for_each_entry(tncur, lsthead, llink) {
if (tncur->ctx == ctx &&
(tncur->cookie == cookie || ++call_nests > EP_MAX_NESTS)) {
/*
* Ops ... loop detected or maximum nest level reached.
* We abort this wake by breaking the cycle itself.
*/
error = -1;
goto out_unlock;
}
}
/* Add the current task and cookie to the list */
tnode.ctx = ctx;
tnode.cookie = cookie;
list_add(&tnode.llink, lsthead);
spin_unlock_irqrestore(&ncalls->lock, flags);
/* Call the nested function */
error = (*nproc)(priv, cookie, call_nests);
/* Remove the current task from the list */
spin_lock_irqsave(&ncalls->lock, flags);
list_del(&tnode.llink);
out_unlock:
spin_unlock_irqrestore(&ncalls->lock, flags);
return error;
}
/*
* As described in commit 0ccf831cb lockdep: annotate epoll
* the use of wait queues used by epoll is done in a very controlled
* manner. Wake ups can nest inside each other, but are never done
* with the same locking. For example:
*
* dfd = socket(...);
* efd1 = epoll_create();
* efd2 = epoll_create();
* epoll_ctl(efd1, EPOLL_CTL_ADD, dfd, ...);
* epoll_ctl(efd2, EPOLL_CTL_ADD, efd1, ...);
*
* When a packet arrives to the device underneath "dfd", the net code will
* issue a wake_up() on its poll wake list. Epoll (efd1) has installed a
* callback wakeup entry on that queue, and the wake_up() performed by the
* "dfd" net code will end up in ep_poll_callback(). At this point epoll
* (efd1) notices that it may have some event ready, so it needs to wake up
* the waiters on its poll wait list (efd2). So it calls ep_poll_safewake()
* that ends up in another wake_up(), after having checked about the
* recursion constraints. That are, no more than EP_MAX_POLLWAKE_NESTS, to
* avoid stack blasting.
*
* When CONFIG_DEBUG_LOCK_ALLOC is enabled, make sure lockdep can handle
* this special case of epoll.
*/
#ifdef CONFIG_DEBUG_LOCK_ALLOC
static struct nested_calls poll_safewake_ncalls;
static int ep_poll_wakeup_proc(void *priv, void *cookie, int call_nests)
{
unsigned long flags;
wait_queue_head_t *wqueue = (wait_queue_head_t *)cookie;
spin_lock_irqsave_nested(&wqueue->lock, flags, call_nests + 1);
wake_up_locked_poll(wqueue, EPOLLIN);
spin_unlock_irqrestore(&wqueue->lock, flags);
return 0;
}
static void ep_poll_safewake(wait_queue_head_t *wq)
{
int this_cpu = get_cpu();
ep_call_nested(&poll_safewake_ncalls,
ep_poll_wakeup_proc, NULL, wq, (void *) (long) this_cpu);
put_cpu();
}
#else
static void ep_poll_safewake(wait_queue_head_t *wq)
{
wake_up_poll(wq, EPOLLIN);
}
#endif
static void ep_remove_wait_queue(struct eppoll_entry *pwq)
{
wait_queue_head_t *whead;
rcu_read_lock();
/*
* If it is cleared by POLLFREE, it should be rcu-safe.
* If we read NULL we need a barrier paired with
* smp_store_release() in ep_poll_callback(), otherwise
* we rely on whead->lock.
*/
whead = smp_load_acquire(&pwq->whead);
if (whead)
remove_wait_queue(whead, &pwq->wait);
rcu_read_unlock();
}
/*
* This function unregisters poll callbacks from the associated file
* descriptor. Must be called with "mtx" held (or "epmutex" if called from
* ep_free).
*/
static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi)
{
struct list_head *lsthead = &epi->pwqlist;
struct eppoll_entry *pwq;
while (!list_empty(lsthead)) {
pwq = list_first_entry(lsthead, struct eppoll_entry, llink);
list_del(&pwq->llink);
ep_remove_wait_queue(pwq);
kmem_cache_free(pwq_cache, pwq);
}
}
/* call only when ep->mtx is held */
static inline struct wakeup_source *ep_wakeup_source(struct epitem *epi)
{
return rcu_dereference_check(epi->ws, lockdep_is_held(&epi->ep->mtx));
}
/* call only when ep->mtx is held */
static inline void ep_pm_stay_awake(struct epitem *epi)
{
struct wakeup_source *ws = ep_wakeup_source(epi);
if (ws)
__pm_stay_awake(ws);
}
static inline bool ep_has_wakeup_source(struct epitem *epi)
{
return rcu_access_pointer(epi->ws) ? true : false;
}
/* call when ep->mtx cannot be held (ep_poll_callback) */
static inline void ep_pm_stay_awake_rcu(struct epitem *epi)
{
struct wakeup_source *ws;
rcu_read_lock();
ws = rcu_dereference(epi->ws);
if (ws)
__pm_stay_awake(ws);
rcu_read_unlock();
}
/**
* ep_scan_ready_list - Scans the ready list in a way that makes possible for
* the scan code, to call f_op->poll(). Also allows for
* O(NumReady) performance.
*
* @ep: Pointer to the epoll private data structure.
* @sproc: Pointer to the scan callback.
* @priv: Private opaque data passed to the @sproc callback.
* @depth: The current depth of recursive f_op->poll calls.
* @ep_locked: caller already holds ep->mtx
*
* Returns: The same integer error code returned by the @sproc callback.
*/
static __poll_t ep_scan_ready_list(struct eventpoll *ep,
__poll_t (*sproc)(struct eventpoll *,
struct list_head *, void *),
void *priv, int depth, bool ep_locked)
{
__poll_t res;
int pwake = 0;
struct epitem *epi, *nepi;
LIST_HEAD(txlist);
lockdep_assert_irqs_enabled();
/*
* We need to lock this because we could be hit by
* eventpoll_release_file() and epoll_ctl().
*/
if (!ep_locked)
mutex_lock_nested(&ep->mtx, depth);
/*
* Steal the ready list, and re-init the original one to the
* empty list. Also, set ep->ovflist to NULL so that events
* happening while looping w/out locks, are not lost. We cannot
* have the poll callback to queue directly on ep->rdllist,
* because we want the "sproc" callback to be able to do it
* in a lockless way.
*/
write_lock_irq(&ep->lock);
list_splice_init(&ep->rdllist, &txlist);
WRITE_ONCE(ep->ovflist, NULL);
write_unlock_irq(&ep->lock);
/*
* Now call the callback function.
*/
res = (*sproc)(ep, &txlist, priv);
write_lock_irq(&ep->lock);
/*
* During the time we spent inside the "sproc" callback, some
* other events might have been queued by the poll callback.
* We re-insert them inside the main ready-list here.
*/
for (nepi = READ_ONCE(ep->ovflist); (epi = nepi) != NULL;
nepi = epi->next, epi->next = EP_UNACTIVE_PTR) {
/*
* We need to check if the item is already in the list.
* During the "sproc" callback execution time, items are
* queued into ->ovflist but the "txlist" might already
* contain them, and the list_splice() below takes care of them.
*/
if (!ep_is_linked(epi)) {
/*
* ->ovflist is LIFO, so we have to reverse it in order
* to keep in FIFO.
*/
list_add(&epi->rdllink, &ep->rdllist);
ep_pm_stay_awake(epi);
}
}
/*
* We need to set back ep->ovflist to EP_UNACTIVE_PTR, so that after
* releasing the lock, events will be queued in the normal way inside
* ep->rdllist.
*/
WRITE_ONCE(ep->ovflist, EP_UNACTIVE_PTR);
/*
* Quickly re-inject items left on "txlist".
*/
list_splice(&txlist, &ep->rdllist);
__pm_relax(ep->ws);
if (!list_empty(&ep->rdllist)) {
/*
* Wake up (if active) both the eventpoll wait list and
* the ->poll() wait list (delayed after we release the lock).
*/
if (waitqueue_active(&ep->wq))
wake_up(&ep->wq);
if (waitqueue_active(&ep->poll_wait))
pwake++;
}
write_unlock_irq(&ep->lock);
if (!ep_locked)
mutex_unlock(&ep->mtx);
/* We have to call this outside the lock */
if (pwake)
ep_poll_safewake(&ep->poll_wait);
return res;
}
static void epi_rcu_free(struct rcu_head *head)
{
struct epitem *epi = container_of(head, struct epitem, rcu);
kmem_cache_free(epi_cache, epi);
}
/*
* Removes a "struct epitem" from the eventpoll RB tree and deallocates
* all the associated resources. Must be called with "mtx" held.
*/
static int ep_remove(struct eventpoll *ep, struct epitem *epi)
{
struct file *file = epi->ffd.file;
lockdep_assert_irqs_enabled();
/*
* Removes poll wait queue hooks.
*/
ep_unregister_pollwait(ep, epi);
/* Remove the current item from the list of epoll hooks */
spin_lock(&file->f_lock);
list_del_rcu(&epi->fllink);
spin_unlock(&file->f_lock);
rb_erase_cached(&epi->rbn, &ep->rbr);
write_lock_irq(&ep->lock);
if (ep_is_linked(epi))
list_del_init(&epi->rdllink);
write_unlock_irq(&ep->lock);
wakeup_source_unregister(ep_wakeup_source(epi));
/*
* At this point it is safe to free the eventpoll item. Use the union
* field epi->rcu, since we are trying to minimize the size of
* 'struct epitem'. The 'rbn' field is no longer in use. Protected by
* ep->mtx. The rcu read side, reverse_path_check_proc(), does not make
* use of the rbn field.
*/
call_rcu(&epi->rcu, epi_rcu_free);
atomic_long_dec(&ep->user->epoll_watches);
return 0;
}
static void ep_free(struct eventpoll *ep)
{
struct rb_node *rbp;
struct epitem *epi;
/* We need to release all tasks waiting for these file */
if (waitqueue_active(&ep->poll_wait))
ep_poll_safewake(&ep->poll_wait);
/*
* We need to lock this because we could be hit by
* eventpoll_release_file() while we're freeing the "struct eventpoll".
* We do not need to hold "ep->mtx" here because the epoll file
* is on the way to be removed and no one has references to it
* anymore. The only hit might come from eventpoll_release_file() but
* holding "epmutex" is sufficient here.
*/
mutex_lock(&epmutex);
/*
* Walks through the whole tree by unregistering poll callbacks.
*/
for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) {
epi = rb_entry(rbp, struct epitem, rbn);
ep_unregister_pollwait(ep, epi);
cond_resched();
}
/*
* Walks through the whole tree by freeing each "struct epitem". At this
* point we are sure no poll callbacks will be lingering around, and also by
* holding "epmutex" we can be sure that no file cleanup code will hit
* us during this operation. So we can avoid the lock on "ep->lock".
* We do not need to lock ep->mtx, either, we only do it to prevent
* a lockdep warning.
*/
mutex_lock(&ep->mtx);
while ((rbp = rb_first_cached(&ep->rbr)) != NULL) {
epi = rb_entry(rbp, struct epitem, rbn);
ep_remove(ep, epi);
cond_resched();
}
mutex_unlock(&ep->mtx);
mutex_unlock(&epmutex);
mutex_destroy(&ep->mtx);
free_uid(ep->user);
wakeup_source_unregister(ep->ws);
kfree(ep);
}
static int ep_eventpoll_release(struct inode *inode, struct file *file)
{
struct eventpoll *ep = file->private_data;
if (ep)
ep_free(ep);
return 0;
}
static __poll_t ep_read_events_proc(struct eventpoll *ep, struct list_head *head,
void *priv);
static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,
poll_table *pt);
/*
* Differs from ep_eventpoll_poll() in that internal callers already have
* the ep->mtx so we need to start from depth=1, such that mutex_lock_nested()
* is correctly annotated.
*/
static __poll_t ep_item_poll(const struct epitem *epi, poll_table *pt,
int depth)
{
struct eventpoll *ep;
bool locked;
pt->_key = epi->event.events;
if (!is_file_epoll(epi->ffd.file))
return vfs_poll(epi->ffd.file, pt) & epi->event.events;
ep = epi->ffd.file->private_data;
poll_wait(epi->ffd.file, &ep->poll_wait, pt);
locked = pt && (pt->_qproc == ep_ptable_queue_proc);
return ep_scan_ready_list(epi->ffd.file->private_data,
ep_read_events_proc, &depth, depth,
locked) & epi->event.events;
}
static __poll_t ep_read_events_proc(struct eventpoll *ep, struct list_head *head,
void *priv)
{
struct epitem *epi, *tmp;
poll_table pt;
int depth = *(int *)priv;
init_poll_funcptr(&pt, NULL);
depth++;
list_for_each_entry_safe(epi, tmp, head, rdllink) {
if (ep_item_poll(epi, &pt, depth)) {
return EPOLLIN | EPOLLRDNORM;
} else {
/*
* Item has been dropped into the ready list by the poll
* callback, but it's not actually ready, as far as
* caller requested events goes. We can remove it here.
*/
__pm_relax(ep_wakeup_source(epi));
list_del_init(&epi->rdllink);
}
}
return 0;
}
static __poll_t ep_eventpoll_poll(struct file *file, poll_table *wait)
{
struct eventpoll *ep = file->private_data;
int depth = 0;
/* Insert inside our poll wait queue */
poll_wait(file, &ep->poll_wait, wait);
/*
* Proceed to find out if wanted events are really available inside
* the ready list.
*/
return ep_scan_ready_list(ep, ep_read_events_proc,
&depth, depth, false);
}
#ifdef CONFIG_PROC_FS
static void ep_show_fdinfo(struct seq_file *m, struct file *f)
{
struct eventpoll *ep = f->private_data;
struct rb_node *rbp;
mutex_lock(&ep->mtx);
for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) {
struct epitem *epi = rb_entry(rbp, struct epitem, rbn);
struct inode *inode = file_inode(epi->ffd.file);
seq_printf(m, "tfd: %8d events: %8x data: %16llx "
" pos:%lli ino:%lx sdev:%x\n",
epi->ffd.fd, epi->event.events,
(long long)epi->event.data,
(long long)epi->ffd.file->f_pos,
inode->i_ino, inode->i_sb->s_dev);
if (seq_has_overflowed(m))
break;
}
mutex_unlock(&ep->mtx);
}
#endif
/* File callbacks that implement the eventpoll file behaviour */
static const struct file_operations eventpoll_fops = {
#ifdef CONFIG_PROC_FS
.show_fdinfo = ep_show_fdinfo,
#endif
.release = ep_eventpoll_release,
.poll = ep_eventpoll_poll,
.llseek = noop_llseek,
};
/*
* This is called from eventpoll_release() to unlink files from the eventpoll
* interface. We need to have this facility to cleanup correctly files that are
* closed without being removed from the eventpoll interface.
*/
void eventpoll_release_file(struct file *file)
{
struct eventpoll *ep;
struct epitem *epi, *next;
/*
* We don't want to get "file->f_lock" because it is not
* necessary. It is not necessary because we're in the "struct file"
* cleanup path, and this means that no one is using this file anymore.
* So, for example, epoll_ctl() cannot hit here since if we reach this
* point, the file counter already went to zero and fget() would fail.
* The only hit might come from ep_free() but by holding the mutex
* will correctly serialize the operation. We do need to acquire
* "ep->mtx" after "epmutex" because ep_remove() requires it when called
* from anywhere but ep_free().
*
* Besides, ep_remove() acquires the lock, so we can't hold it here.
*/
mutex_lock(&epmutex);
list_for_each_entry_safe(epi, next, &file->f_ep_links, fllink) {
ep = epi->ep;
mutex_lock_nested(&ep->mtx, 0);
ep_remove(ep, epi);
mutex_unlock(&ep->mtx);
}
mutex_unlock(&epmutex);
}
static int ep_alloc(struct eventpoll **pep)
{
int error;
struct user_struct *user;
struct eventpoll *ep;
user = get_current_user();
error = -ENOMEM;
ep = kzalloc(sizeof(*ep), GFP_KERNEL);
if (unlikely(!ep))
goto free_uid;
mutex_init(&ep->mtx);
rwlock_init(&ep->lock);
init_waitqueue_head(&ep->wq);
init_waitqueue_head(&ep->poll_wait);
INIT_LIST_HEAD(&ep->rdllist);
ep->rbr = RB_ROOT_CACHED;
ep->ovflist = EP_UNACTIVE_PTR;
ep->user = user;
*pep = ep;
return 0;
free_uid:
free_uid(user);
return error;
}
/*
* Search the file inside the eventpoll tree. The RB tree operations
* are protected by the "mtx" mutex, and ep_find() must be called with
* "mtx" held.
*/
static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd)
{
int kcmp;
struct rb_node *rbp;
struct epitem *epi, *epir = NULL;
struct epoll_filefd ffd;
ep_set_ffd(&ffd, file, fd);
for (rbp = ep->rbr.rb_root.rb_node; rbp; ) {
epi = rb_entry(rbp, struct epitem, rbn);
kcmp = ep_cmp_ffd(&ffd, &epi->ffd);
if (kcmp > 0)
rbp = rbp->rb_right;
else if (kcmp < 0)
rbp = rbp->rb_left;
else {
epir = epi;
break;
}
}
return epir;
}
#ifdef CONFIG_CHECKPOINT_RESTORE
static struct epitem *ep_find_tfd(struct eventpoll *ep, int tfd, unsigned long toff)
{
struct rb_node *rbp;
struct epitem *epi;
for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) {
epi = rb_entry(rbp, struct epitem, rbn);
if (epi->ffd.fd == tfd) {
if (toff == 0)
return epi;
else
toff--;
}
cond_resched();
}
return NULL;
}
struct file *get_epoll_tfile_raw_ptr(struct file *file, int tfd,
unsigned long toff)
{
struct file *file_raw;
struct eventpoll *ep;
struct epitem *epi;
if (!is_file_epoll(file))
return ERR_PTR(-EINVAL);
ep = file->private_data;
mutex_lock(&ep->mtx);
epi = ep_find_tfd(ep, tfd, toff);
if (epi)
file_raw = epi->ffd.file;
else
file_raw = ERR_PTR(-ENOENT);
mutex_unlock(&ep->mtx);
return file_raw;
}
#endif /* CONFIG_CHECKPOINT_RESTORE */
/**
* Adds a new entry to the tail of the list in a lockless way, i.e.
* multiple CPUs are allowed to call this function concurrently.
*
* Beware: it is necessary to prevent any other modifications of the
* existing list until all changes are completed, in other words
* concurrent list_add_tail_lockless() calls should be protected
* with a read lock, where write lock acts as a barrier which
* makes sure all list_add_tail_lockless() calls are fully
* completed.
*
* Also an element can be locklessly added to the list only in one
* direction i.e. either to the tail either to the head, otherwise
* concurrent access will corrupt the list.
*
* Returns %false if element has been already added to the list, %true
* otherwise.
*/
static inline bool list_add_tail_lockless(struct list_head *new,
struct list_head *head)
{
struct list_head *prev;
/*
* This is simple 'new->next = head' operation, but cmpxchg()
* is used in order to detect that same element has been just
* added to the list from another CPU: the winner observes
* new->next == new.
*/
if (cmpxchg(&new->next, new, head) != new)
return false;
/*
* Initially ->next of a new element must be updated with the head
* (we are inserting to the tail) and only then pointers are atomically
* exchanged. XCHG guarantees memory ordering, thus ->next should be
* updated before pointers are actually swapped and pointers are
* swapped before prev->next is updated.
*/
prev = xchg(&head->prev, new);
/*
* It is safe to modify prev->next and new->prev, because a new element
* is added only to the tail and new->next is updated before XCHG.
*/
prev->next = new;
new->prev = prev;
return true;
}
/**
* Chains a new epi entry to the tail of the ep->ovflist in a lockless way,
* i.e. multiple CPUs are allowed to call this function concurrently.
*
* Returns %false if epi element has been already chained, %true otherwise.
*/
static inline bool chain_epi_lockless(struct epitem *epi)
{
struct eventpoll *ep = epi->ep;
/* Check that the same epi has not been just chained from another CPU */
if (cmpxchg(&epi->next, EP_UNACTIVE_PTR, NULL) != EP_UNACTIVE_PTR)
return false;
/* Atomically exchange tail */
epi->next = xchg(&ep->ovflist, epi);
return true;
}
/*
* This is the callback that is passed to the wait queue wakeup
* mechanism. It is called by the stored file descriptors when they
* have events to report.
*
* This callback takes a read lock in order not to content with concurrent
* events from another file descriptors, thus all modifications to ->rdllist
* or ->ovflist are lockless. Read lock is paired with the write lock from
* ep_scan_ready_list(), which stops all list modifications and guarantees
* that lists state is seen correctly.
*
* Another thing worth to mention is that ep_poll_callback() can be called
* concurrently for the same @epi from different CPUs if poll table was inited
* with several wait queues entries. Plural wakeup from different CPUs of a
* single wait queue is serialized by wq.lock, but the case when multiple wait
* queues are used should be detected accordingly. This is detected using
* cmpxchg() operation.
*/
static int ep_poll_callback(wait_queue_entry_t *wait, unsigned mode, int sync, void *key)
{
int pwake = 0;
struct epitem *epi = ep_item_from_wait(wait);
struct eventpoll *ep = epi->ep;
__poll_t pollflags = key_to_poll(key);
unsigned long flags;
int ewake = 0;
read_lock_irqsave(&ep->lock, flags);
ep_set_busy_poll_napi_id(epi);
/*
* If the event mask does not contain any poll(2) event, we consider the
* descriptor to be disabled. This condition is likely the effect of the
* EPOLLONESHOT bit that disables the descriptor when an event is received,
* until the next EPOLL_CTL_MOD will be issued.
*/
if (!(epi->event.events & ~EP_PRIVATE_BITS))
goto out_unlock;
/*
* Check the events coming with the callback. At this stage, not
* every device reports the events in the "key" parameter of the
* callback. We need to be able to handle both cases here, hence the
* test for "key" != NULL before the event match test.
*/
if (pollflags && !(pollflags & epi->event.events))
goto out_unlock;
/*
* If we are transferring events to userspace, we can hold no locks
* (because we're accessing user memory, and because of linux f_op->poll()
* semantics). All the events that happen during that period of time are
* chained in ep->ovflist and requeued later on.
*/
if (READ_ONCE(ep->ovflist) != EP_UNACTIVE_PTR) {
if (epi->next == EP_UNACTIVE_PTR &&
chain_epi_lockless(epi))
ep_pm_stay_awake_rcu(epi);
goto out_unlock;
}
/* If this file is already in the ready list we exit soon */
if (!ep_is_linked(epi) &&
list_add_tail_lockless(&epi->rdllink, &ep->rdllist)) {
ep_pm_stay_awake_rcu(epi);
}
/*
* Wake up ( if active ) both the eventpoll wait list and the ->poll()
* wait list.
*/
if (waitqueue_active(&ep->wq)) {
if ((epi->event.events & EPOLLEXCLUSIVE) &&
!(pollflags & POLLFREE)) {
switch (pollflags & EPOLLINOUT_BITS) {
case EPOLLIN:
if (epi->event.events & EPOLLIN)
ewake = 1;
break;
case EPOLLOUT:
if (epi->event.events & EPOLLOUT)
ewake = 1;
break;
case 0:
ewake = 1;
break;
}
}
wake_up(&ep->wq);
}
if (waitqueue_active(&ep->poll_wait))
pwake++;
out_unlock:
read_unlock_irqrestore(&ep->lock, flags);
/* We have to call this outside the lock */
if (pwake)
ep_poll_safewake(&ep->poll_wait);
if (!(epi->event.events & EPOLLEXCLUSIVE))
ewake = 1;
if (pollflags & POLLFREE) {
/*
* If we race with ep_remove_wait_queue() it can miss
* ->whead = NULL and do another remove_wait_queue() after
* us, so we can't use __remove_wait_queue().
*/
list_del_init(&wait->entry);
/*
* ->whead != NULL protects us from the race with ep_free()
* or ep_remove(), ep_remove_wait_queue() takes whead->lock
* held by the caller. Once we nullify it, nothing protects
* ep/epi or even wait.
*/
smp_store_release(&ep_pwq_from_wait(wait)->whead, NULL);
}
return ewake;
}
/*
* This is the callback that is used to add our wait queue to the
* target file wakeup lists.
*/
static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,
poll_table *pt)
{
struct epitem *epi = ep_item_from_epqueue(pt);
struct eppoll_entry *pwq;
if (epi->nwait >= 0 && (pwq = kmem_cache_alloc(pwq_cache, GFP_KERNEL))) {
init_waitqueue_func_entry(&pwq->wait, ep_poll_callback);
pwq->whead = whead;
pwq->base = epi;
if (epi->event.events & EPOLLEXCLUSIVE)
add_wait_queue_exclusive(whead, &pwq->wait);
else
add_wait_queue(whead, &pwq->wait);
list_add_tail(&pwq->llink, &epi->pwqlist);
epi->nwait++;
} else {
/* We have to signal that an error occurred */
epi->nwait = -1;
}
}
static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi)
{
int kcmp;
struct rb_node **p = &ep->rbr.rb_root.rb_node, *parent = NULL;
struct epitem *epic;
bool leftmost = true;
while (*p) {
parent = *p;
epic = rb_entry(parent, struct epitem, rbn);
kcmp = ep_cmp_ffd(&epi->ffd, &epic->ffd);
if (kcmp > 0) {
p = &parent->rb_right;
leftmost = false;
} else
p = &parent->rb_left;
}
rb_link_node(&epi->rbn, parent, p);
rb_insert_color_cached(&epi->rbn, &ep->rbr, leftmost);
}
#define PATH_ARR_SIZE 5
/*
* These are the number paths of length 1 to 5, that we are allowing to emanate
* from a single file of interest. For example, we allow 1000 paths of length
* 1, to emanate from each file of interest. This essentially represents the
* potential wakeup paths, which need to be limited in order to avoid massive
* uncontrolled wakeup storms. The common use case should be a single ep which
* is connected to n file sources. In this case each file source has 1 path
* of length 1. Thus, the numbers below should be more than sufficient. These
* path limits are enforced during an EPOLL_CTL_ADD operation, since a modify
* and delete can't add additional paths. Protected by the epmutex.
*/
static const int path_limits[PATH_ARR_SIZE] = { 1000, 500, 100, 50, 10 };
static int path_count[PATH_ARR_SIZE];
static int path_count_inc(int nests)
{
/* Allow an arbitrary number of depth 1 paths */
if (nests == 0)
return 0;
if (++path_count[nests] > path_limits[nests])
return -1;
return 0;
}
static void path_count_init(void)
{
int i;
for (i = 0; i < PATH_ARR_SIZE; i++)
path_count[i] = 0;
}
static int reverse_path_check_proc(void *priv, void *cookie, int call_nests)
{
int error = 0;
struct file *file = priv;
struct file *child_file;
struct epitem *epi;
/* CTL_DEL can remove links here, but that can't increase our count */
rcu_read_lock();
list_for_each_entry_rcu(epi, &file->f_ep_links, fllink) {
child_file = epi->ep->file;
if (is_file_epoll(child_file)) {
if (list_empty(&child_file->f_ep_links)) {
if (path_count_inc(call_nests)) {
error = -1;
break;
}
} else {
error = ep_call_nested(&poll_loop_ncalls,
reverse_path_check_proc,
child_file, child_file,
current);
}
if (error != 0)
break;
} else {
printk(KERN_ERR "reverse_path_check_proc: "
"file is not an ep!\n");
}
}
rcu_read_unlock();
return error;
}
/**
* reverse_path_check - The tfile_check_list is list of file *, which have
* links that are proposed to be newly added. We need to
* make sure that those added links don't add too many
* paths such that we will spend all our time waking up
* eventpoll objects.
*
* Returns: Returns zero if the proposed links don't create too many paths,
* -1 otherwise.
*/
static int reverse_path_check(void)
{
int error = 0;
struct file *current_file;
/* let's call this for all tfiles */
list_for_each_entry(current_file, &tfile_check_list, f_tfile_llink) {
path_count_init();
error = ep_call_nested(&poll_loop_ncalls,
reverse_path_check_proc, current_file,
current_file, current);
if (error)
break;
}
return error;
}
static int ep_create_wakeup_source(struct epitem *epi)
{
const char *name;
struct wakeup_source *ws;
if (!epi->ep->ws) {
epi->ep->ws = wakeup_source_register("eventpoll");
if (!epi->ep->ws)
return -ENOMEM;
}
name = epi->ffd.file->f_path.dentry->d_name.name;
ws = wakeup_source_register(name);
if (!ws)
return -ENOMEM;
rcu_assign_pointer(epi->ws, ws);
return 0;
}
/* rare code path, only used when EPOLL_CTL_MOD removes a wakeup source */
static noinline void ep_destroy_wakeup_source(struct epitem *epi)
{
struct wakeup_source *ws = ep_wakeup_source(epi);
RCU_INIT_POINTER(epi->ws, NULL);
/*
* wait for ep_pm_stay_awake_rcu to finish, synchronize_rcu is
* used internally by wakeup_source_remove, too (called by
* wakeup_source_unregister), so we cannot use call_rcu
*/
synchronize_rcu();
wakeup_source_unregister(ws);
}
/*
* Must be called with "mtx" held.
*/
static int ep_insert(struct eventpoll *ep, const struct epoll_event *event,
struct file *tfile, int fd, int full_check)
{
int error, pwake = 0;
__poll_t revents;
long user_watches;
struct epitem *epi;
struct ep_pqueue epq;
lockdep_assert_irqs_enabled();
user_watches = atomic_long_read(&ep->user->epoll_watches);
if (unlikely(user_watches >= max_user_watches))
return -ENOSPC;
if (!(epi = kmem_cache_alloc(epi_cache, GFP_KERNEL)))
return -ENOMEM;
/* Item initialization follow here ... */
INIT_LIST_HEAD(&epi->rdllink);
INIT_LIST_HEAD(&epi->fllink);
INIT_LIST_HEAD(&epi->pwqlist);
epi->ep = ep;
ep_set_ffd(&epi->ffd, tfile, fd);
epi->event = *event;
epi->nwait = 0;
epi->next = EP_UNACTIVE_PTR;
if (epi->event.events & EPOLLWAKEUP) {
error = ep_create_wakeup_source(epi);
if (error)
goto error_create_wakeup_source;
} else {
RCU_INIT_POINTER(epi->ws, NULL);
}
/* Initialize the poll table using the queue callback */
epq.epi = epi;
init_poll_funcptr(&epq.pt, ep_ptable_queue_proc);
/*
* Attach the item to the poll hooks and get current event bits.
* We can safely use the file* here because its usage count has
* been increased by the caller of this function. Note that after
* this operation completes, the poll callback can start hitting
* the new item.
*/
revents = ep_item_poll(epi, &epq.pt, 1);
/*
* We have to check if something went wrong during the poll wait queue
* install process. Namely an allocation for a wait queue failed due
* high memory pressure.
*/
error = -ENOMEM;
if (epi->nwait < 0)
goto error_unregister;
/* Add the current item to the list of active epoll hook for this file */
spin_lock(&tfile->f_lock);
list_add_tail_rcu(&epi->fllink, &tfile->f_ep_links);
spin_unlock(&tfile->f_lock);
/*
* Add the current item to the RB tree. All RB tree operations are
* protected by "mtx", and ep_insert() is called with "mtx" held.
*/
ep_rbtree_insert(ep, epi);
/* now check if we've created too many backpaths */
error = -EINVAL;
if (full_check && reverse_path_check())
goto error_remove_epi;
/* We have to drop the new item inside our item list to keep track of it */
write_lock_irq(&ep->lock);
/* record NAPI ID of new item if present */
ep_set_busy_poll_napi_id(epi);
/* If the file is already "ready" we drop it inside the ready list */
if (revents && !ep_is_linked(epi)) {
list_add_tail(&epi->rdllink, &ep->rdllist);
ep_pm_stay_awake(epi);
/* Notify waiting tasks that events are available */
if (waitqueue_active(&ep->wq))
wake_up(&ep->wq);
if (waitqueue_active(&ep->poll_wait))
pwake++;
}
write_unlock_irq(&ep->lock);
atomic_long_inc(&ep->user->epoll_watches);
/* We have to call this outside the lock */
if (pwake)
ep_poll_safewake(&ep->poll_wait);
return 0;
error_remove_epi:
spin_lock(&tfile->f_lock);
list_del_rcu(&epi->fllink);
spin_unlock(&tfile->f_lock);
rb_erase_cached(&epi->rbn, &ep->rbr);
error_unregister:
ep_unregister_pollwait(ep, epi);
/*
* We need to do this because an event could have been arrived on some
* allocated wait queue. Note that we don't care about the ep->ovflist
* list, since that is used/cleaned only inside a section bound by "mtx".
* And ep_insert() is called with "mtx" held.
*/
write_lock_irq(&ep->lock);
if (ep_is_linked(epi))
list_del_init(&epi->rdllink);
write_unlock_irq(&ep->lock);
wakeup_source_unregister(ep_wakeup_source(epi));
error_create_wakeup_source:
kmem_cache_free(epi_cache, epi);
return error;
}
/*
* Modify the interest event mask by dropping an event if the new mask
* has a match in the current file status. Must be called with "mtx" held.
*/
static int ep_modify(struct eventpoll *ep, struct epitem *epi,
const struct epoll_event *event)
{
int pwake = 0;
poll_table pt;
lockdep_assert_irqs_enabled();
init_poll_funcptr(&pt, NULL);
/*
* Set the new event interest mask before calling f_op->poll();
* otherwise we might miss an event that happens between the
* f_op->poll() call and the new event set registering.
*/
epi->event.events = event->events; /* need barrier below */
epi->event.data = event->data; /* protected by mtx */
if (epi->event.events & EPOLLWAKEUP) {
if (!ep_has_wakeup_source(epi))
ep_create_wakeup_source(epi);
} else if (ep_has_wakeup_source(epi)) {
ep_destroy_wakeup_source(epi);
}
/*
* The following barrier has two effects:
*
* 1) Flush epi changes above to other CPUs. This ensures
* we do not miss events from ep_poll_callback if an
* event occurs immediately after we call f_op->poll().
* We need this because we did not take ep->lock while
* changing epi above (but ep_poll_callback does take
* ep->lock).
*
* 2) We also need to ensure we do not miss _past_ events
* when calling f_op->poll(). This barrier also
* pairs with the barrier in wq_has_sleeper (see
* comments for wq_has_sleeper).
*
* This barrier will now guarantee ep_poll_callback or f_op->poll
* (or both) will notice the readiness of an item.
*/
smp_mb();
/*
* Get current event bits. We can safely use the file* here because
* its usage count has been increased by the caller of this function.
* If the item is "hot" and it is not registered inside the ready
* list, push it inside.
*/
if (ep_item_poll(epi, &pt, 1)) {
write_lock_irq(&ep->lock);
if (!ep_is_linked(epi)) {
list_add_tail(&epi->rdllink, &ep->rdllist);
ep_pm_stay_awake(epi);
/* Notify waiting tasks that events are available */
if (waitqueue_active(&ep->wq))
wake_up(&ep->wq);
if (waitqueue_active(&ep->poll_wait))
pwake++;
}
write_unlock_irq(&ep->lock);
}
/* We have to call this outside the lock */
if (pwake)
ep_poll_safewake(&ep->poll_wait);
return 0;
}
static __poll_t ep_send_events_proc(struct eventpoll *ep, struct list_head *head,
void *priv)
{
struct ep_send_events_data *esed = priv;
__poll_t revents;
struct epitem *epi, *tmp;
struct epoll_event __user *uevent = esed->events;
struct wakeup_source *ws;
poll_table pt;
init_poll_funcptr(&pt, NULL);
esed->res = 0;
/*
* We can loop without lock because we are passed a task private list.
* Items cannot vanish during the loop because ep_scan_ready_list() is
* holding "mtx" during this call.
*/
lockdep_assert_held(&ep->mtx);
list_for_each_entry_safe(epi, tmp, head, rdllink) {
if (esed->res >= esed->maxevents)
break;
/*
* Activate ep->ws before deactivating epi->ws to prevent
* triggering auto-suspend here (in case we reactive epi->ws
* below).
*
* This could be rearranged to delay the deactivation of epi->ws
* instead, but then epi->ws would temporarily be out of sync
* with ep_is_linked().
*/
ws = ep_wakeup_source(epi);
if (ws) {
if (ws->active)
__pm_stay_awake(ep->ws);
__pm_relax(ws);
}
list_del_init(&epi->rdllink);
/*
* If the event mask intersect the caller-requested one,
* deliver the event to userspace. Again, ep_scan_ready_list()
* is holding ep->mtx, so no operations coming from userspace
* can change the item.
*/
revents = ep_item_poll(epi, &pt, 1);
if (!revents)
continue;
if (__put_user(revents, &uevent->events) ||
__put_user(epi->event.data, &uevent->data)) {
list_add(&epi->rdllink, head);
ep_pm_stay_awake(epi);
if (!esed->res)
esed->res = -EFAULT;
return 0;
}
esed->res++;
uevent++;
if (epi->event.events & EPOLLONESHOT)
epi->event.events &= EP_PRIVATE_BITS;
else if (!(epi->event.events & EPOLLET)) {
/*
* If this file has been added with Level
* Trigger mode, we need to insert back inside
* the ready list, so that the next call to
* epoll_wait() will check again the events
* availability. At this point, no one can insert
* into ep->rdllist besides us. The epoll_ctl()
* callers are locked out by
* ep_scan_ready_list() holding "mtx" and the
* poll callback will queue them in ep->ovflist.
*/
list_add_tail(&epi->rdllink, &ep->rdllist);
ep_pm_stay_awake(epi);
}
}
return 0;
}
static int ep_send_events(struct eventpoll *ep,
struct epoll_event __user *events, int maxevents)
{
struct ep_send_events_data esed;
esed.maxevents = maxevents;
esed.events = events;
ep_scan_ready_list(ep, ep_send_events_proc, &esed, 0, false);
return esed.res;
}
static inline struct timespec64 ep_set_mstimeout(long ms)
{
struct timespec64 now, ts = {
.tv_sec = ms / MSEC_PER_SEC,
.tv_nsec = NSEC_PER_MSEC * (ms % MSEC_PER_SEC),
};
ktime_get_ts64(&now);
return timespec64_add_safe(now, ts);
}
/**
* ep_poll - Retrieves ready events, and delivers them to the caller supplied
* event buffer.
*
* @ep: Pointer to the eventpoll context.
* @events: Pointer to the userspace buffer where the ready events should be
* stored.
* @maxevents: Size (in terms of number of events) of the caller event buffer.
* @timeout: Maximum timeout for the ready events fetch operation, in
* milliseconds. If the @timeout is zero, the function will not block,
* while if the @timeout is less than zero, the function will block
* until at least one event has been retrieved (or an error
* occurred).
*
* Returns: Returns the number of ready events which have been fetched, or an
* error code, in case of error.
*/
static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
int maxevents, long timeout)
{
int res = 0, eavail, timed_out = 0;
u64 slack = 0;
bool waiter = false;
wait_queue_entry_t wait;
ktime_t expires, *to = NULL;
lockdep_assert_irqs_enabled();
if (timeout > 0) {
struct timespec64 end_time = ep_set_mstimeout(timeout);
slack = select_estimate_accuracy(&end_time);
to = &expires;
*to = timespec64_to_ktime(end_time);
} else if (timeout == 0) {
/*
* Avoid the unnecessary trip to the wait queue loop, if the
* caller specified a non blocking operation. We still need
* lock because we could race and not see an epi being added
* to the ready list while in irq callback. Thus incorrectly
* returning 0 back to userspace.
*/
timed_out = 1;
write_lock_irq(&ep->lock);
eavail = ep_events_available(ep);
write_unlock_irq(&ep->lock);
goto send_events;
}
fetch_events:
if (!ep_events_available(ep))
ep_busy_loop(ep, timed_out);
eavail = ep_events_available(ep);
if (eavail)
goto send_events;
/*
* Busy poll timed out. Drop NAPI ID for now, we can add
* it back in when we have moved a socket with a valid NAPI
* ID onto the ready list.
*/
ep_reset_busy_poll_napi_id(ep);
/*
* We don't have any available event to return to the caller. We need
* to sleep here, and we will be woken by ep_poll_callback() when events
* become available.
*/
if (!waiter) {
waiter = true;
init_waitqueue_entry(&wait, current);
spin_lock_irq(&ep->wq.lock);
__add_wait_queue_exclusive(&ep->wq, &wait);
spin_unlock_irq(&ep->wq.lock);
}
for (;;) {
/*
* We don't want to sleep if the ep_poll_callback() sends us
* a wakeup in between. That's why we set the task state
* to TASK_INTERRUPTIBLE before doing the checks.
*/
set_current_state(TASK_INTERRUPTIBLE);
/*
* Always short-circuit for fatal signals to allow
* threads to make a timely exit without the chance of
* finding more events available and fetching
* repeatedly.
*/
if (fatal_signal_pending(current)) {
res = -EINTR;
break;
}
eavail = ep_events_available(ep);
if (eavail)
break;
if (signal_pending(current)) {
res = -EINTR;
break;
}
if (!schedule_hrtimeout_range(to, slack, HRTIMER_MODE_ABS)) {
timed_out = 1;
break;
}
}
__set_current_state(TASK_RUNNING);
send_events:
/*
* Try to transfer events to user space. In case we get 0 events and
* there's still timeout left over, we go trying again in search of
* more luck.
*/
if (!res && eavail &&
!(res = ep_send_events(ep, events, maxevents)) && !timed_out)
goto fetch_events;
if (waiter) {
spin_lock_irq(&ep->wq.lock);
__remove_wait_queue(&ep->wq, &wait);
spin_unlock_irq(&ep->wq.lock);
}
return res;
}
/**
* ep_loop_check_proc - Callback function to be passed to the @ep_call_nested()
* API, to verify that adding an epoll file inside another
* epoll structure, does not violate the constraints, in
* terms of closed loops, or too deep chains (which can
* result in excessive stack usage).
*
* @priv: Pointer to the epoll file to be currently checked.
* @cookie: Original cookie for this call. This is the top-of-the-chain epoll
* data structure pointer.
* @call_nests: Current dept of the @ep_call_nested() call stack.
*
* Returns: Returns zero if adding the epoll @file inside current epoll
* structure @ep does not violate the constraints, or -1 otherwise.
*/
static int ep_loop_check_proc(void *priv, void *cookie, int call_nests)
{
int error = 0;
struct file *file = priv;
struct eventpoll *ep = file->private_data;
struct eventpoll *ep_tovisit;
struct rb_node *rbp;
struct epitem *epi;
mutex_lock_nested(&ep->mtx, call_nests + 1);
ep->visited = 1;
list_add(&ep->visited_list_link, &visited_list);
for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) {
epi = rb_entry(rbp, struct epitem, rbn);
if (unlikely(is_file_epoll(epi->ffd.file))) {
ep_tovisit = epi->ffd.file->private_data;
if (ep_tovisit->visited)
continue;
error = ep_call_nested(&poll_loop_ncalls,
ep_loop_check_proc, epi->ffd.file,
ep_tovisit, current);
if (error != 0)
break;
} else {
/*
* If we've reached a file that is not associated with
* an ep, then we need to check if the newly added
* links are going to add too many wakeup paths. We do
* this by adding it to the tfile_check_list, if it's
* not already there, and calling reverse_path_check()
* during ep_insert().
*/
if (list_empty(&epi->ffd.file->f_tfile_llink))
list_add(&epi->ffd.file->f_tfile_llink,
&tfile_check_list);
}
}
mutex_unlock(&ep->mtx);
return error;
}
/**
* ep_loop_check - Performs a check to verify that adding an epoll file (@file)
* another epoll file (represented by @ep) does not create
* closed loops or too deep chains.
*
* @ep: Pointer to the epoll private data structure.
* @file: Pointer to the epoll file to be checked.
*
* Returns: Returns zero if adding the epoll @file inside current epoll
* structure @ep does not violate the constraints, or -1 otherwise.
*/
static int ep_loop_check(struct eventpoll *ep, struct file *file)
{
int ret;
struct eventpoll *ep_cur, *ep_next;
ret = ep_call_nested(&poll_loop_ncalls,
ep_loop_check_proc, file, ep, current);
/* clear visited list */
list_for_each_entry_safe(ep_cur, ep_next, &visited_list,
visited_list_link) {
ep_cur->visited = 0;
list_del(&ep_cur->visited_list_link);
}
return ret;
}
static void clear_tfile_check_list(void)
{
struct file *file;
/* first clear the tfile_check_list */
while (!list_empty(&tfile_check_list)) {
file = list_first_entry(&tfile_check_list, struct file,
f_tfile_llink);
list_del_init(&file->f_tfile_llink);
}
INIT_LIST_HEAD(&tfile_check_list);
}
/*
* Open an eventpoll file descriptor.
*/
static int do_epoll_create(int flags)
{
int error, fd;
struct eventpoll *ep = NULL;
struct file *file;
/* Check the EPOLL_* constant for consistency. */
BUILD_BUG_ON(EPOLL_CLOEXEC != O_CLOEXEC);
if (flags & ~EPOLL_CLOEXEC)
return -EINVAL;
/*
* Create the internal data structure ("struct eventpoll").
*/
error = ep_alloc(&ep);
if (error < 0)
return error;
/*
* Creates all the items needed to setup an eventpoll file. That is,
* a file structure and a free file descriptor.
*/
fd = get_unused_fd_flags(O_RDWR | (flags & O_CLOEXEC));
if (fd < 0) {
error = fd;
goto out_free_ep;
}
file = anon_inode_getfile("[eventpoll]", &eventpoll_fops, ep,
O_RDWR | (flags & O_CLOEXEC));
if (IS_ERR(file)) {
error = PTR_ERR(file);
goto out_free_fd;
}
ep->file = file;
fd_install(fd, file);
return fd;
out_free_fd:
put_unused_fd(fd);
out_free_ep:
ep_free(ep);
return error;
}
SYSCALL_DEFINE1(epoll_create1, int, flags)
{
return do_epoll_create(flags);
}
SYSCALL_DEFINE1(epoll_create, int, size)
{
if (size <= 0)
return -EINVAL;
return do_epoll_create(0);
}
/*
* The following function implements the controller interface for
* the eventpoll file that enables the insertion/removal/change of
* file descriptors inside the interest set.
*/
SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
struct epoll_event __user *, event)
{
int error;
int full_check = 0;
struct fd f, tf;
struct eventpoll *ep;
struct epitem *epi;
struct epoll_event epds;
struct eventpoll *tep = NULL;
error = -EFAULT;
if (ep_op_has_event(op) &&
copy_from_user(&epds, event, sizeof(struct epoll_event)))
goto error_return;
error = -EBADF;
f = fdget(epfd);
if (!f.file)
goto error_return;
/* Get the "struct file *" for the target file */
tf = fdget(fd);
if (!tf.file)
goto error_fput;
/* The target file descriptor must support poll */
error = -EPERM;
if (!file_can_poll(tf.file))
goto error_tgt_fput;
/* Check if EPOLLWAKEUP is allowed */
if (ep_op_has_event(op))
ep_take_care_of_epollwakeup(&epds);
/*
* We have to check that the file structure underneath the file descriptor
* the user passed to us _is_ an eventpoll file. And also we do not permit
* adding an epoll file descriptor inside itself.
*/
error = -EINVAL;
if (f.file == tf.file || !is_file_epoll(f.file))
goto error_tgt_fput;
/*
* epoll adds to the wakeup queue at EPOLL_CTL_ADD time only,
* so EPOLLEXCLUSIVE is not allowed for a EPOLL_CTL_MOD operation.
* Also, we do not currently supported nested exclusive wakeups.
*/
if (ep_op_has_event(op) && (epds.events & EPOLLEXCLUSIVE)) {
if (op == EPOLL_CTL_MOD)
goto error_tgt_fput;
if (op == EPOLL_CTL_ADD && (is_file_epoll(tf.file) ||
(epds.events & ~EPOLLEXCLUSIVE_OK_BITS)))
goto error_tgt_fput;
}
/*
* At this point it is safe to assume that the "private_data" contains
* our own data structure.
*/
ep = f.file->private_data;
/*
* When we insert an epoll file descriptor, inside another epoll file
* descriptor, there is the change of creating closed loops, which are
* better be handled here, than in more critical paths. While we are
* checking for loops we also determine the list of files reachable
* and hang them on the tfile_check_list, so we can check that we
* haven't created too many possible wakeup paths.
*
* We do not need to take the global 'epumutex' on EPOLL_CTL_ADD when
* the epoll file descriptor is attaching directly to a wakeup source,
* unless the epoll file descriptor is nested. The purpose of taking the
* 'epmutex' on add is to prevent complex toplogies such as loops and
* deep wakeup paths from forming in parallel through multiple
* EPOLL_CTL_ADD operations.
*/
mutex_lock_nested(&ep->mtx, 0);
if (op == EPOLL_CTL_ADD) {
if (!list_empty(&f.file->f_ep_links) ||
is_file_epoll(tf.file)) {
full_check = 1;
mutex_unlock(&ep->mtx);
mutex_lock(&epmutex);
if (is_file_epoll(tf.file)) {
error = -ELOOP;
if (ep_loop_check(ep, tf.file) != 0) {
clear_tfile_check_list();
goto error_tgt_fput;
}
} else
list_add(&tf.file->f_tfile_llink,
&tfile_check_list);
mutex_lock_nested(&ep->mtx, 0);
if (is_file_epoll(tf.file)) {
tep = tf.file->private_data;
mutex_lock_nested(&tep->mtx, 1);
}
}
}
/*
* Try to lookup the file inside our RB tree, Since we grabbed "mtx"
* above, we can be sure to be able to use the item looked up by
* ep_find() till we release the mutex.
*/
epi = ep_find(ep, tf.file, fd);
error = -EINVAL;
switch (op) {
case EPOLL_CTL_ADD:
if (!epi) {
epds.events |= EPOLLERR | EPOLLHUP;
error = ep_insert(ep, &epds, tf.file, fd, full_check);
} else
error = -EEXIST;
if (full_check)
clear_tfile_check_list();
break;
case EPOLL_CTL_DEL:
if (epi)
error = ep_remove(ep, epi);
else
error = -ENOENT;
break;
case EPOLL_CTL_MOD:
if (epi) {
if (!(epi->event.events & EPOLLEXCLUSIVE)) {
epds.events |= EPOLLERR | EPOLLHUP;
error = ep_modify(ep, epi, &epds);
}
} else
error = -ENOENT;
break;
}
if (tep != NULL)
mutex_unlock(&tep->mtx);
mutex_unlock(&ep->mtx);
error_tgt_fput:
if (full_check)
mutex_unlock(&epmutex);
fdput(tf);
error_fput:
fdput(f);
error_return:
return error;
}
/*
* Implement the event wait interface for the eventpoll file. It is the kernel
* part of the user space epoll_wait(2).
*/
static int do_epoll_wait(int epfd, struct epoll_event __user *events,
int maxevents, int timeout)
{
int error;
struct fd f;
struct eventpoll *ep;
/* The maximum number of event must be greater than zero */
if (maxevents <= 0 || maxevents > EP_MAX_EVENTS)
return -EINVAL;
/* Verify that the area passed by the user is writeable */
if (!access_ok(events, maxevents * sizeof(struct epoll_event)))
return -EFAULT;
/* Get the "struct file *" for the eventpoll file */
f = fdget(epfd);
if (!f.file)
return -EBADF;
/*
* We have to check that the file structure underneath the fd
* the user passed to us _is_ an eventpoll file.
*/
error = -EINVAL;
if (!is_file_epoll(f.file))
goto error_fput;
/*
* At this point it is safe to assume that the "private_data" contains
* our own data structure.
*/
ep = f.file->private_data;
/* Time to fish for events ... */
error = ep_poll(ep, events, maxevents, timeout);
error_fput:
fdput(f);
return error;
}
SYSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events,
int, maxevents, int, timeout)
{
return do_epoll_wait(epfd, events, maxevents, timeout);
}
/*
* Implement the event wait interface for the eventpoll file. It is the kernel
* part of the user space epoll_pwait(2).
*/
SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events,
int, maxevents, int, timeout, const sigset_t __user *, sigmask,
size_t, sigsetsize)
{
int error;
sigset_t ksigmask, sigsaved;
/*
* If the caller wants a certain signal mask to be set during the wait,
* we apply it here.
*/
error = set_user_sigmask(sigmask, &ksigmask, &sigsaved, sigsetsize);
if (error)
return error;
error = do_epoll_wait(epfd, events, maxevents, timeout);
restore_user_sigmask(sigmask, &sigsaved);
return error;
}
#ifdef CONFIG_COMPAT
COMPAT_SYSCALL_DEFINE6(epoll_pwait, int, epfd,
struct epoll_event __user *, events,
int, maxevents, int, timeout,
const compat_sigset_t __user *, sigmask,
compat_size_t, sigsetsize)
{
long err;
sigset_t ksigmask, sigsaved;
/*
* If the caller wants a certain signal mask to be set during the wait,
* we apply it here.
*/
err = set_compat_user_sigmask(sigmask, &ksigmask, &sigsaved, sigsetsize);
if (err)
return err;
err = do_epoll_wait(epfd, events, maxevents, timeout);
restore_user_sigmask(sigmask, &sigsaved);
return err;
}
#endif
static int __init eventpoll_init(void)
{
struct sysinfo si;
si_meminfo(&si);
/*
* Allows top 4% of lomem to be allocated for epoll watches (per user).
*/
max_user_watches = (((si.totalram - si.totalhigh) / 25) << PAGE_SHIFT) /
EP_ITEM_COST;
BUG_ON(max_user_watches < 0);
/*
* Initialize the structure used to perform epoll file descriptor
* inclusion loops checks.
*/
ep_nested_calls_init(&poll_loop_ncalls);
#ifdef CONFIG_DEBUG_LOCK_ALLOC
/* Initialize the structure used to perform safe poll wait head wake ups */
ep_nested_calls_init(&poll_safewake_ncalls);
#endif
/*
* We can have many thousands of epitems, so prevent this from
* using an extra cache line on 64-bit (and smaller) CPUs
*/
BUILD_BUG_ON(sizeof(void *) <= 8 && sizeof(struct epitem) > 128);
/* Allocates slab cache used to allocate "struct epitem" items */
epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem),
0, SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT, NULL);
/* Allocates slab cache used to allocate "struct eppoll_entry" */
pwq_cache = kmem_cache_create("eventpoll_pwq",
sizeof(struct eppoll_entry), 0, SLAB_PANIC|SLAB_ACCOUNT, NULL);
return 0;
}
fs_initcall(eventpoll_init);